Many techniques have been proposed and practised for measuring the electric power being supplied to a load. One type of metering apparatus is shown in U.S. Pat. No. 2,269,225 Jan. 6, 1942 (Rich). The patent describes a clamp-on type current sensor and a hook-on reistance type voltage sensor to measure voltage, current and reactive power of an overhead high voltage transmission line.
U.S. Pat. No. 4,348,638 Sept. 7, 1982 (Baldridge, Jr.) measures the current flowing into the load by means of a transformer secondary winding toroidally wrapped around one of the two parallel mains. No considerations are given to the Poynting vector.
The Poynting vector has been suggested for the measurement of energy transfer in electromagnetic devices. Thus in an article authored by the inventor of the present application, "Measurement of Losses in Saturated Solid Magnetic Cores", IEEE Trans. on Magnetics, Vol. MAG-7, No. 1, March 1971, pp 198-201, a new method of measuring the losses in saturated solid magnetic cores subjected to alternating magnetization is described. The method is based on the measurement of an alternative Poynting vector in the region between the surface of the iron core and the magnetizing winding. The two constituents of this power-flow vector are the partial electric field and the magnetic field.
In an article also authored by the present inventor, "Direct Measurement of the Fundamental and Harmonic Tooth-Ripple Losses in Solid Poles, Part II: Experimental investigation" IEEE Trans on Power Apparatus and Systems, Vol. PAS-90, No. 2, March/April 1971, pp 602-610, the experimental results of power flow measurements in the air gap of a salient-pole synchronous machine at no-load in the rotor references frame are reported. Suitable probes for measuring the electric and magnetic field componentsin the air gap of the machine are described together with the associated electric circuits. This technique has enabled the direct measurement of the tooth-ripple loss due to each individual harmonic in an ordinary machine and under actual running conditions where all the harmonics are simultaneously present. In another article by W. Z. Fam et al, "On the Measurement of Tooth-Rippled Losses in Laminated Poles" IEEE Trans. on Instrumentation and Measurement, Vol. IM-22, No. 1, March 1973, pp. 88-92, the method was applied to loss measurement in laminated poles.
Still another way of measuring the power is discussed in an article, "A Frequency-Compensated High-Voltage Current-Comparator-based Capacitance Bridge for Shunt Reactor Loss Measurement" by E. So, IEEE Trans on Instrumentation and Measurement, Vol IM-31, pp 46-49, March 1982. In this article, the power is determined by measuring the complementary phase angle .delta. using a modified current-comparator-based compacitance bridge. However, this method is very complex and is not a direct measurement of electric power requiring several expensive high precision components such as compressed-gas high-voltage capacitor, current-comparator etc.
Unlike prior art devices known to the inventor, some of which are described above, the present invention permits the direct measurement of electric power supplied by a source of power to a load. The probe to carry out the present method is very compact, simple and inexpensive to manufacture.